Saw-tooth wave generator



Dec. 21, 1948. LEE 2,456,961

v SAW-TOOTH WAVE GENERATOR U Filed Sept. 12, 1946 2 Sheets-Sheet 1 l AA WITN ESSES: INVENTOR Eeuben Lee BY 4 9 W ATTORNE Dec. 21, 1948. I R L55 2,456,961

SAW-TOOTH YIAVE GENERATOR Filed Sept. 12 1946 2 sheets-sheet 2 WITNESSES: INVENTOR W M Pe /ban Lee.

. 1 ATTORN Y Patented Dec. 21, 1948 NI TED STAT ES JPAT E N T OFFICE "S AW T-GOTH WAVE GENERATOR Reuben Lee, Linthicum Heights, Md assignor to Westinghouse -'Elec'tric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania *Application September 12, 1946, S'c'ri'alNo. 696,574

5 Claims. 1

=My invention relates to oscillation generators and, in particular, to a new type of oscillation generator particularly adapted to the production "of sawtooth wave forms.

One object of my invention is to produce a generator for sharply peaked Waves which shall he of a highdegree of stability inrespect to frequency and amplitude.

Another object of my invention is to provide a generator .of waves of the general sawtooth form which .shall involve only relatively simple circuit elements.

Another object of my invention :is to provide a generator for sawtooth waves in which the waveslope is to a high degree rectilinear.

Still another object of any invention is to pro- *vide an arrangement for generating sawtooth waves which shall employ only alternating-cur- '-ren't'generators of substantially pur'e sine waves in combination witha circuit involving Jrectifiers.

A further object of my invention is to provide a sawtooth wave generator theoutput of which shall have a wave form of substahtially' linear ne'gative slope.

Other objects of my invention will become apparent upon reading "the following description taken in connection with the accompanying draw- Bags, in which:

Figures 1, 2, '6 and '7 are graphs showing the waveform produced "by-certain circuits embodying the principles of my invention;

Fig. 3 Ba circuit diagram of an embodiment of my invention; and

Figs. 4, 5, 8 and 9 are diagrams o'f-cer'tain circuit networks whichmay be employed in carrying out the principles of my invention.

Fig. 1'0 is a circuit diagram combining the net- 'work of Fig. *8 with the voltage source 01 Fig. 3.

Referring in detail to the drawing, the curve marked e1 in Fig. 1 shows a plotin which the abscissae represent time and the ordinates amplitude of the output voltage of an ideal full-wave rectifier when the input voltage thereto is an ideal pure/sine wave. In order to obtain 'anoutput "voltage of the form c1 it is necessary that the circui'tsof the rectifier shall have the least practicable leakageinductance and stray capacitance.

The curve 62 in Fig. 1 issimply the reverse of the curve e1 displaced slightly in phase relative thereto; in other words, it illustrates the Wave .form of the outputo'f asimilar full-wave rectifier so connected as 'to produce current i of the opposite polarity to the rectifier producing thecurve c1, and supplied from asine wave alternator which Ill lags slightly :in phase relative to that supplyln the rectifier of output e1.

When the ordinates of the curves @1 and ez'fof Fig. 1 are added together, a curve of the "wave -form es shown in Fig. 2 results. It will be noted thatin Fig. 2 the downward slope of the curve :is not -:exactly rectilinear, but that the 'curve gives a fair approximation to a sawtooth wave. Varying the phase displacement between the curves 1 and ez willchangethe amount of the departure of the down. slope from rectilinearity and will also changethe' amplitude of the peaks and troughs of the wave, and the ratio of up-slope to-doWn-slope. Howeventhe curve e3 in-Fig. Zprobably represents about the best approximation to a rectilinear down-slope that can be obtained, with the phase displacement between curves er and 92 suchas to give steep up-slope.

A circuit network capable of producing voltage of the wave form e; is shown in Fig. 3 where an ordinary'high vacuum triode 'I has its plate cireuitlprovided with an anti-resonant tuned network comprising an inductance 2 and a capacitance-3 and likewise has its grid circuit provided with aself-biascircuit comprising a resistance '4 and a capacitance 5. 'In a manner well known in the electronics art, the grid circuit and the plate circuit of 'thetube l 'are'magnetically inter- 'linked, for example, by locating the inductance "2 and an inductancefi in' the grid circuit in mutually inductive relation "to each other. The circuit l to '6 will be recognized as an ordinary feed-back oscillator, and such oscillators can be made by well known methods of adjustment to produce output voltages which approximate very closely tothe sine wave form. This particular type of oscillator is "to be taken merely as s'ymbolical 'of "any suitable sine 'wavegenerator known in the'art. An output coil 1, inductively linked with the iloa'dicircuit .ofthe oscillator "l is connected to two ltran'sformer primariesia, 9. Ase'condary H' associated with the primary winding 8 has its end terminals connected through. a pair of recti'fiers l2, 13 which may, for example, be high-vacuum diodes, or, alternatively, be copper oxide rectifiers or any other suitable type of rectifier. The :primary winding 9 is associated with a secondary winding 44 across the terminals of which are serially connected a variable resistor f5 and a capacitor [6. The common terminal of "the resistor l5 and the capacitor 16 is connected to one terminal of a primary winding l1, theotlfer terminal of which is connected to "the mid point of the winding I'4. A'secon'dar'y winding "l'afas'sociated with the primary winding 11, has its'enfd terminals connected to a pair of rectifiers l9, 2! which may be of the same general type as the rectifiers l2, l3 already mentioned. The mid point of the secondary winding I! is connected to the mid point of the secondary winding l8, and the common terminals of the rectifiers l2, l3 are connected to one side 22 of an output circuit in which it is desired to use a wave form of the type shown in Fig. 2, the other terminal of this output circuit being connected to a line 23 connected to the common terminal of the rectifiers l9, 2i.

It will be recognized that the resistor I and the capacitor it constitute a phase-displacing circuit by which the alternating voltage impressed on the primary winding ll may be displaced to any desired degree relative to the alternating voltage impressed on the primary winding 8. By properly designing, in ways which will be evident to those skilled in the art, the size of the transformer windings above mentioned or, alternatively, by properly adjusting the resistor l5 and capacitor I5, the relative amplitudes and phase of the rectified voltage waves produced respectively by the rectifiers l2, l3 and I9, 2| may be adjusted at will. A moments consideration of the above-described circuit will show that the rectifiers l2, l3 will produce an output voltage similar to er in Fig. 1, while the rectifiers l9, 2| will produce a rectified voltage of opposite polarity displaced in phase relative to the output of rectifiers l2, l3, and hence a voltage similar to ea in Fig. 1 across the terminals of the rectifiers l9, 2 I. A voltage will be produced across the line wires 22, 23, which will have the wave form shown in the curve es in Fig. 2.

In Fig. 4, I show an alternative form of network which may be connected to the output of rectifiers I2, l3 and I9, 2! in Fig. 3 to produce a wave form of the type shown in Fig. 2. When the arrangement shown in Fig. 4 is to be used, the line wire connecting the mid points of secondary windings I! and i8 is broken. A moments consideration willshow that between the mid point of the secondary winding II and the common terminal 22 of rectifiers I2, i3 is produced a'voltage of the form cu in Fig. 1, while a voltage of the wave form eg in Fig. 1 is produced between the output terminal 23 and the mid point of the winding [8 in Fig. 3. The terminal 22 and the line leading to the mid point of winding H in Fig. 3 are then connected between the terminals 2t, 25 in the network shown in Fig. 4, while the terminal 23 and the mid point of the secondary winding 68 in Fig. 3 are connected, respectively, to the terminals 25 and 21 in Fig. 4. Between the terminals 24 and 21 in Fig. 4 are serially connected a pair of impedances 2B, 29 which may be resistors, while a third impedance 3i which may likewise be a resistor, is connected between the mid points of the impedances 28,29 and the line interconnecting terminals 25 and 26 in Fig. 4. A moments consideration will show that the voltage across the terminals of the impedance 31 will be the algebraic difference of the voltages er and e; of Fig. 1; in other words, the voltage across the impedance 3! will have the wave form a; shown in Fig. 2.

If a voltage of the wave form e1 of Fig. 1 is connected across a capacitance 32 in series with a resistance 33, as shown in Fig. 5, the. wave form across the resistance 33 will be of the type shown in Fig. 6. It will be noted that the downward -linear but is curved in a sense opposite to the curvature of the down slope of voltage es in Fig. 2.

across the branches 59 and 61.

The degree of departure of the down slopes in Fig. 6 from rectilinearity is a function of the relative magnitudes of the capacitor 32 and the resistor 33 in Fig. 5.

Since the curvature of the down slope in Fig. 6 is the reverse of the curvature in the down slope of the voltage ea in Fig. 2,it will be evident that by properly proportioning the size'of the capacitor 32 and the resistor 33 in Fig. 5, it will be possible to cause the curvature in the down slope of the curve a; of Fig. 6 to exactly compensate for the reverse curvature in the down slope of the curve e; in Fig. 2 if the voltages es and er are added together in a circuit. When this is done, a curve of the form e5 shown in Fig. 7 in which both the up-slope and down-slope of the wave are almost exactly rectilinear will be obtained.

Fig. 8 shows a network in which the voltages of the wave form as and er are properly added together to obtain a wave form of the type shown in Fig. 7. Thus the output voltage e1 between the terminal 22 and the mid point of secondary winding II in Fig. 3 may be connected across the terminals 3d, 35 in the network shown in Fig. 8, while the output Voltage (22 appearing between the terminal 23 and the mid point of winding IS in Fig. 3 is connected across the terminals 36, 3'! in Fig. 8. Between the terminals 33 and 31 in Fig. 8 are connected a pair of impedances 38, 39 which may, for example, be resistors. The impedance 38 is shunted by a variable capacitor 4!. The common terminal of the impedances 38 and 39 is connected through an impedance 42, which may be a resistor, to the line interconnecting the terminals 35 and 36.

It will be noted that the resistor 38 and capacitor 4! may be considered together to constitute an impedance.

A moments consideration of the circuits of Fig. 8 will show that the current traversing the impedance 42 is the difference between the output currents set up therein by voltages similar to e; of Fig. 6 and as of Fig. 1 which, as already shown, results in a wave form as of the ideally rectilinear shape shown in Fig. '7. A voltage of the wave form es can thus be derived from a pair of tap points on the impedance 42.

Another network is shown in Fig. 9. In this case one branch includes a parallel network 5! of an inductance 53 and a condenser 55 connected in series with a resistor 51; a second branch consists of the resistor 59 and the third branch of the resistor 6 I The voltage an is impressed across the branches 51-51 and 59 and the voltage e2 The sawtooth voltage e5 having a wave form of linear negative slope is derived across the resistor 53.

With the rectified voltages c1 and ez derived from a 60 cycle supply, a voltage es of wave form, the negative slope branch of which is linear, was derived with components as follows in the branches of the circuit shown in Fig. 9.

Inductance 53 between 5 and 10 henries Capacity 55 between .33 and .66 mid. Resistance 57 10,000 ohms Resistance 59 200 ohms Resistance 61 10,000 ohms While, in accordance with the patent statutes, I have illustrated particular embodiments of my invention, it will be recognized by those skilled in the art that the principles thereof are of broad application in ways which-will be evident to them.

I claim as my invention:

1. In combination with a source of sine wave alternating currents, a first full-wave rectifier supplied therefrom, a second full-wave rectifier supplied with a phase-displaced sine wave voltage of the same frequency as that first mentioned, a network comprising a pair of impedances connected in series in one side of a line with a third impedance connected between the common ter.. minal of the two first-mentioned impedances and the other side of the line, and means for connecting the output of the first-mentioned rectifier to one pair of end terminals of said network and for connecting the other said rectifier to the other end terminals of said network.

2. In combination with a source of sine wave alternatin currents, a first full-wave rectifier supplied therefrom, a second full-wave rectifier supplied with a phase-displaced sine wave voltage of the same frequency as that first mentioned, a network comprising a pair of impedances of similar sign connected in series in one side of a line with a third impedance of the same sign connected between the common terminal of the two first-mentioned impedances and the other side of the line, and means for connecting the output of the first-mentioned rectifier to one pair of end terminals of said network and for connecting the other said rectifier to the other end terminals of said network.

3. In combination with a source of sine wave voltage, a first full-wave rectifier supplied from said source, a second full-wave rectifier supplied with sine wave current of the same frequency as said source, but phase displaced relative thereto, a network having four terminals, a resistor shunted by a capacitor connected in series with a second resistor between a first and a second of said terminals, an impedance connecting the common terminal of said capacitor and said second re- 6 sister with both the third and fourth of said terminals, means for connecting the output of the first-mentioned rectifier to the first and third of said terminals, and means for connecting the output of said second rectifier to the second and fourth of said terminals,

4. In combination with a feed-back oscillator, a first rectifier supplied with the output voltage of said oscillator, a second rectifier fed through a phase-displacing network with the output voltage of said oscillator, a network comprising four terminals, the first and third of said terminals being connected by a channel comprising a first resistor shunted by a capacitor in series with a second resistor, an impedance connecting the common terminal of said capacitor and said second resistor with the second and fourth of said terminals, and means for connecting said first rectifier across said first and second terminals and for connecting said second rectifier across the third and fourth terminals.

5. In combination a first full-wave rectifier, having input and output terminals, va 'second fullwave rectifier, having input and output termirials, means for impressing sinusoidal oscillations of substantially the same wave form on said input terminals of both said rectifiers, means for displacing the outputs of said rectifiers in phase, means for combinin the outputs of said rectifiers so displaced in phase in such manner that one output is subtracted from the other output and means for so distorting oneof'said outputs that the combined output has a wave form the negative slope branch of which is substantially linear.

REUBEN LEE.

No references cited. 

